This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-25983, filed Feb. 1, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a novel material exhibiting a third-order nonlinear optical property. More specifically, the present invention relates to a porphyrin array having bis(imidazolyl porphyrin metal complex) as structural unit thereof, which array exhibiting excellent third-order nonlinear optical properties.
2. Description of the Related Art
A third-order nonlinear optical material is essentially required for the development of optical fast optical switch and an optical modulation element. However, in order to employ such a third-order nonlinear optical material in actual applications, it is considered that the performance of the material, converted and expressed as the value of third-order susceptibility ("khgr"(3)), must be enhanced by the order of three digits or so, as compared with the organic materials which have been reported. When an organic compound exhibiting significant nonlinearity is designed, it is important that the polarizability of the molecule is increased by increasing the degree of overlap of the orbitals by expanding the xcfx80 electron conjugate system, and by combining an electron donor with an electron acceptor.
Porphyrin is a cyclic tetrapyrrole in which four pyrrole nucleuses are alternatively bridged by four methine groups and has a large conjugate system constituted of 18xcfx80 electrons. Due to this, porphyrin has been studied as a nonlinear optical material. In the conventional study, Anderson reported that the one-dimensional linear porphyrin array, in which free base or metalloporphyrins are connected to each other with butadiyne bonds, exhibits more large nonlinearity, as compared with the porphyrin complex monomer (Chem. Phys., 248, 181 (1999)). However, in this case, the length of the resulting polymer cannot be regulated due to the use of tile covalent bonds. Further, as neither introduction of a hetero metal thereto nor introduction of a donor or acceptor at the terminal substituent thereof is easy, the nonlinear property of the resulting polymer cannot be improved any further. On the other hand, Osuka et al. synthesized a one-dimensional linear porphyrin array in which free base or metalloporphyrins are directly connected to each other at the meso position thereof and a one-dimensional linear porphyrin array in which the porphyrin complexes are bridged to each other with phenylene groups, and measured the degree of nonlinearity of the synthesized porphyrin structures. However, as the donor or acceptor is not introduced thereto, the resulting polymer of Osuga et al. failed to exhibit a significantly large nonlinear property (J. Appl. Phys., 81, 2946 (1997)). In short, it is difficult, by using a covalent bond, to introduce a donor and an acceptor which should provide a high polarizability to a one-dimensional linear porphyrin array. Therefore, significantly large nonlinear property cannot be realized by the conventional method of synthesizing a porphyrin array.
An object of the present invention is to provide a material that exhibits a third-order nonlinear optical response of a significantly large magnitude.
Another object of the present invention is to provide a method of producing such a material.
In order to attain the objects described above, the inventors of the present invention synthesized a novel porphyrin dimer consisting of a metal complex of porphyrin having an imidazolyl group and porphyrin having an imidazolyl group but no metal (hereinafter this dimer is referred to as a mono-metal porphyrin complex dimer). The inventors found that the mono-metal porphyrin complex dimer can be a terminal molecule of the porphyrin array, and serves as an electron donor and acceptor. Specifically, the metal complex of porphyrin having an imidazolyl group serves as a donor and the porphyrin having an imidazolyl group but no metal serves as an acceptor.
The inventors had discovered, prior to the synthesis of the mono-metal porphyrin complex dimer described above, that by coordinating a nitrogen atom of an imidazolyl group of one imidazolyl porphyrin metal complex to the metal atom of another imidazolyl porphyrin metal complex, thereby forming bridges between the porphyrin complexes, a porphyrin array in which a plurality of imidazolyl porphyrin complex dimers are connected to each other by way of coordinate bonds, can be obtained (hereinafter, the diner consisting of two porphyrin complexes are also referred to as bis-porphyrin complex diner). The inventors also discovered that, in a reaction system, the coordinate bonds of the porphyrin array can be cleaved and reconstructed by adding and removing a solvent, such as methanol or pyridine, respectively (JP-A 2001-213883, which corresponds to the allowed U.S. application Ser. No. 09/767,900, and JP-A 2001-253883, which corresponds to a co-pending application Ser. No. 09/802,923).
The inventors found that a mixture of the newly synthesized mono-metal porphyrin complex dimers and a porphyrin array having, as its structural unit, bis-porphyrin complex dimers, may be re-organized in a polar solvent, such as methanol or pyridine, thereby a material exhibiting a significantly large nonlinear optical response can be formed, and accomplished the present invention.
Accordingly, the present invention provides a porphyrin array represented by the following general formula (1-1) or (1-2): 
wherein R1 represents an alkyl group or a substituted or unsubstituted aryl group; M1 represents a metal ion;
R2 and R3 independently represent an electron acceptor or an electron donor, preferably selected from the group consisting of free base porphyrin, gold porphyrin, pyromellitic diimide, dialkylviologen, benzoquinone and ferrocene; Im represents IM1 or Im2 shown below: 
xe2x80x83wherein R4 represents a hydrogen atom or a methyl group); and n represents an integer in the range of 1 to 100.
The present invention also provides a method of producing the porphyrin array represented by the general formula (1-1) or (1-2) of the present invention comprising:
reacting, in the presence of a polar solvent, either one or both of porphyrin metal complexes represented by the general formulae (2-1) and (2-2): 
xe2x80x83wherein R1, R2, R3, M1 and Im have the same meanings as in the general formula (1-1) or (1-2) with bis-porphyrin complex dimer represented by the general formula (3): 
xe2x80x83wherein R1, M1 and Im have the same meanings as in the general formula (1-1).
As an example of the porphyrin metal complex represented by the general formula (2-1) or (2-2), a nono-metal porphyrin complex dimer represented by the general formula (2xe2x80x2) may be used: 
wherein R1, M1 and Im have the same meanings as in the general formulae (1-1).
The porphyrin array represented by the general formula (1-2) may be synthesized by reacting, in the presence of a polar solvent, either one of both of the porphyrin metal complexes represented by the general formulae (2-1) and (2-2). The present invention also provides this method of preparing the porphyrin array represented by the general formula (1-2).
The present invention also provide the porphyrin metal complex represented by the general formula (2-1) or (2-2).
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.